Pipe threading die head assembly



Oct. 8, 1957 K. K. KERR ErAL 2,868,599

. PIPE: THREADING DIE man ASSEMBLY Original Filed Nov. 20, 1951lNvEN-roczfs, KARL K. KERR, EowAQo J. KLEBER, JQ. SAMUEL H.S. RAUB IZ, YBY ATTORNEY United States Patent PIPE THREADING DIE HEAD ASSEMBLY KarlK. Kerr, Lakewood, Ghio, Edward J. Kleber, Jr., Niagara Falls, N. Y.,and Samuel H. S. Raub, hay Village, Ohio, assignors to Union CarbideCorporation, a corporation of New York 1 Claim. (Cl. 1li-123) Thisinvention relates to die heads for pipe threading,l

and, more particularly, to die heads for threading impervious carbon andgraphite pipe. Heretofore, pipe threading has been accomplished by useof standard dies wherein the cutting teeth have a constant pitch andpitch diameter. The iirst few teeth of each chaser of the standard dieheads are truncated to form a throat, so that the thread is generated bya series of teeth of the same pitch diameter, each tooth cutting by thatamount which it projects inwardly further than the preceding tooth. Whensuch dies are used to thread carbon and graphite pipe the threadsgenerated are scratched, scored and ragged due to the fact that eachsucceeding tooth cuts deeper without cleaning up any of the threadsurface generated by the preceding tooth.

It is an object of the present invention to provide a die head that willgenerate threads on pipe without crushing, scratching, or damaging thethread surface.

Another object is to provide a die head that will generate a pipe threadhaving a gradually stepped runout of decreasing pitch diameter in theregion of furthest threadmg.

A further object is to provide for a die head assembly that willgenerate pipe threads without requiring an external force to hold theassembly to the pipe once it has been set thereon preparatory to thecommencement of the threading operation.

A still further object is to provide a die head that will generatesmooth threads on pipe made of highly abrasive material, such asimpervious carbon and graphite.

Other objects and advantages of this invention will be apparent duringthe course of the following description.

In the accompanying drawings:

Fig. 1 is a partial longitudinal sectional view of a hand threading diehead embodying the present invention and engaged pipe in the fullythreaded position;

Fig. 2 is a sectional view taken along the line 9 9 of Fig. 1, the frontplate of the die head having been removed to show the radial arrangementof cutting teeth and sizing nibs, part being broken away; and

Fig. 3 is a partial sectional view of a partly threaded pipeillustrating the effect of variations in cutting tooth pitch diameter.

A die head assembly embodying the present invention is shown in Figs. 1and 2 and comprises a stepped-diameter cylindrical mandrel 1', having atone end a relatively large diameter threaded portion and a relativelyreduced diameter pipe-grasping arbor section 3 at the opposite end. Thepipe-grasping arbor carries a sleeve of rubber or other suitablematerial 5' which expands to grasp the internal surface of pipe P aswing nut 6 is tightened causing a retraction of the front plug ofmandrel 1. The hollow cylindrical die head 7 is mounted axially on themandrel so that the die head moves along the threaded portion of themandrel as it is rotated. In manual operation this rotation of the headmay be accomplished by means of handle 9. The die head 7 supportsradially-positioned vPatented Oct. '8, 1957' chasers 10 which arepositioned around the internal periphery of the die head. Sizing nibs 11are provided for trimming the outside diameter of the pipe.Chasermounted cutting teeth 12 are provided of pitch equal to thethreads of the threaded portion of mandrel 1 which act as pushers tomaintain the proper thread pitch for the cutting teeth 12 as the cuttingteeth generate threads on the work. The cutting teeth 12 areindividually mounted on separate chasers and staggered in position toprovide varying pitch diameters. .A front plate 14 holds the chasers inthe die head.

The chasers are so constructed and arranged that the sizing nibs 1,1turn down the outside diameter of pipe P' to the proper major diameterfor threading before the commencement of the threading operation. Then,as the head is further advanced along the mandrel, the rst cutting toothcuts approximately twenty-tive percent full thread depth. Subsequentteeth, following at intervals, cut to a progressively greater threaddepth with the fifth tooth in sequence cutting to full depth, as shownin Fig. 3 of the drawing. This means that, when using the embodimentshown in the drawings, full thread depth is attained in one and aquarter turns of the die head after the rst tooth has engaged the pipe.

All cutting teeth on the chasers of the die head of the presentinvention are of full tooth shape but of varying pitch diameters. Of thetotal of eight cutting teeth on the embodiment of the present inventionshown in the drawings, only tive actually cut when the die head is new.As these teeth become dull with use and are sharpened, the pitchdiameters are increased and teeth six, seven, and eight take on workprogressively.

In operation, the pipe to be threaded is suitably secured in a vise.Before using the illustrated assembly, the die head 7 is turned back tothe rear of the mandrel 1. The arbor section 3 is then inserted into thepipe up to the front shoulder of the mandrel, and, while the mandrel 1is held stationary, the Wing nut 6 on the end of the mandrel istightened. This causes an expansion of the rubber arbor 3' and securelyholds the die head assembly to the pipe, as is shown in Fig. l.

The actual threading operation is then begun by turning the knobbedhandle 9 in a clockwise direction. This is continued until the head 7contacts stop 17 which resists further turning. When it is desired togenerate greater lengths of thread the stop 17 is removed so'that thedie head 7 may move off mandrel and continue threading the pipe to anydesired point. The die head assembly may be removed after the threadingoperation is completed by backing die head 7' 0E the pipe with acounter-clockwise motion, loosening the wing nut 6 of the handle end ofmandrel 1 and removing the mandrel from the pipe.

The thread generated by the die head of the present invention has agradually stepped runout and not a relief of full depth such as on astandard lathe-chased thread. When the die head of the present inventionis used for threading highly abrasive materials, such as imperviouscarbon or graphite pipe, it has been found advantageous to employ nibsand cutting teeth of sintered carbide, silver soldered, brazed, orotherwise secured into position on the chaser.

This is a division of our copending application Serial No. 257,232 tiledNovember 20, 1951, issued on May 8, 1956, as U. S. Patent 2,744,269.

What is claimed is:

A die head assembly for threading impervious carbon and graphite pipe toany desired length comprising a stepped-diameter cylindrical mandrelhaving a threaded portion near the rear end thereof, a reduced diameterexpandable arbor section at the front end thereof for insertion intosaid pipe, and means for expanding said arbor section to engage theinterior of said pipe; a die head having a plurality of pusher teethpositioned near the rear end thereof and a plurality of pusher teethpositioned near the front end thereof for rotatably engaging saidthreaded portion of said mandrel; a plurality of chasers symmetricallyand circumferentially disposed around and rigidly secured to said diehead; a single cutting tooth separately and rigidly secured to each ofsaid chasers and projecting inwardly in advance of the front endplurality of pusher teeth to cut said pipe, there being a total of atleast five such cutting teeth positioned to cut symmetrically to fullthread prole and successive cutting teeth'arranged to cut progressivelydeeper whereby a thread of full depth is developed on said pipe in lessthan one and one-half revolutions of said die head; said plurality ofdie head pusher teeth having the same pitch as said cutting teeth andapitch diameter equal to the pitch diameter of the cutting teeth whichare positioned to cut said pipe to full depth.

References Cited in the le of this patent UNITED STATES PATENTS1,053,482. Dreier Feb. 18, 1913 2,744,269 Kerr et al, May 8, 1956

